It applies notably to cable-stayed suspensions of bridges. The stays vibrate notably on account of the wind and the movement of vehicles. Different types of device have been proposed for damping these vibrations.
In a first type of damping device (see for example EP 0 343 054 A1, DE 295 17 250 U1 or WO 98/04780 A1), the vibrational energy is dissipated around an individual cable, in a zone delimited radially by an element fixed to the suspended structure. This element may be an arm extending between the cable and the suspended structure, or a tube that holds the lower part of the cable.
Further devices use linear-stroke dampers such as hydraulic cylinders. One or more cylinders may be disposed on one or more arms that connect an individual cable to the suspended structure (see for example JP 09-59921 A) or between the cable and a tube that is fixed to the suspended structure and contains the lower part of the cable (see for example FR 2 859 260 A1 or JP 06-58370 A).
A damping device referred to as a pendular damping device has an oscillating arm connected to the cable, the oscillations of which are damped by viscous friction. FR 2 664 920 A1 describes an example of such a pendular device.
The abovementioned damping devices have the limitation of having to be disposed in the vicinity of the suspended structure, i.e. close to the anchoring point of the cable, typically at a distance that represents 1 to 3% of the total length of the cable.
FR 2 862 073 A1 describes another type of damping device which connects the cable not to a fixed point on the suspended structure but to an adjacent cable. Since the stays of a cable-stayed bridge generally have different lengths, they all have different natural frequencies of vibration. Consequently, during a vibrational episode, there is always a relative movement between the cables. The damping device according to FR 2 862 073 A1 takes advantage of this relative movement in order to dissipate the energy. The adjacent cable thus represents a pseudo fixed point for the vibrating cable.
Although this pseudo fixed point is less effective than an actual fixed point such as the deck of the cable-stayed bridge, these devices are nevertheless very effective, since they can be positioned relatively far away from the anchoring point of the cable, typically 5 to 10% of the total length.
However, this damping device has the limitation of only acting in the plane of the cables that it connects, i.e. in the plane of the plane of stays. Movements out of the plane (transverse movements) are not effectively damped.
In order to combat vibrations of a plane of stays, another method consists in installing cables interconnecting the stays, said cables stiffening the plane of stays transversely and preventing the stays from adopting certain vibrational modes. Although the interconnecting cables can be designed to damp the vertical vibrations in order to supplement the individual damping applied at the root of the stays, they remain virtually without effect on the transverse vibrations.
An object of the present invention to propose a device for damping vibrations in cables, such as the stays of a bridge, which is highly effective in particular for damping transverse vibrations.